Combine whiskey, brown sugar, soy sauce, water, Worcestershire sauce, lemon juice and garlic powder, mix well. Place roast into a plastic bag; add marinade and seal. Place in a dish; refrigerate overnight, turning occasionally. Grill over medium coals (with Jack Daniel's Barrel Chips, soaked in water--if you can find them), about 20 to 25 minutes per side for medium. Baste occasionally with marinade. To serve, cut into thin slices.